1. Technical Field
The invention concerns improved trick mode playback, and more particularly to the display of closed captioned information during trick mode playback of a video presentation.
2. Description of the Related Art
Television signals can include an auxiliary signal component, which can represent information other than video and audio program components of a television program. For example, in the United States, NTSC (National Television Standards Committee) television signals include closed caption information. Closed caption refers to text captions that are the written representation of the audio segment of a video presentation or television program, which are embedded in a video signal, but do not form part of the permanently displayed video. Closed caption requires a special decoder to decode and display the closed caption information. When decoded and displayed, closed captioning provides a visible text representation of a television program's audio content, the text being synchronous with the audio content.
The auxiliary information signal component representing closed caption data comprises two bytes of binary closed caption data during the latter half of each occurrence of line 21 of field 1 of the standardized video display. Additional closed caption data and similarly encoded information, such as extended data services (XDS) information, can be included in other line intervals such as line 21 of field 2. The NTSC standard and U.S. law requires that all television receivers in excess of 13 inches to have integrated decoders and circuitry capable of decoding and displaying closed caption information located on line 21 of the vertical blanking interval (VBI) of video signals. For this reason, practically all video presentations, including but not limited to television broadcasts, digital versatile disks (DVDs), video compact disks (CDs) and videotapes now include captioning data.
Although captioning was developed to aid the hearing impaired, captioning can also provide a benefit to non-hearing-impaired viewers as well. Providing captioning for an auxiliary image in a multi-image display, such as picture-in-picture (PIP) or picture-outside-picture (POP) displays, is an example of this type of additional benefit. For example, activating a PIP feature produces a small image representing the content of a PIP program signal to be displayed in a portion of the main picture. However, only the audio program associated with the main picture is processed and coupled to the speakers of the television. The audio content of the PIP signal is lost. Because the audio program is important to the comprehension of a television program, the usefulness of the PIP feature is severely limited by the lack of an associated audio program. An approach to solving this problem is to display captions, i.e., visible text, representing the PIP audio programming portion of the display. However, the closed caption decoder in most television receivers processes only the caption information associated with the main picture, not the PIP signal. Another solution is to provide multiple televisions tuners each with its own captioning decoder.
Notwithstanding, technological advancements in storage media have resulted in the proliferation of video presentations that have been recorded in a digital format for distribution. For example, DVDs can store video presentation such as full-length motion pictures in the well-known MPEG format for distribution. The MPEG formatted presentation stored on the DVD can include closed captioned, as well as subpicture information. Subpicture information refers to the captions, subtitles, menus, animations, and other information that can be flexibly displayed upon demand or on the occurrence of certain events. Unlike the closed captioned information which is an auxiliary component of the video presentation signal, subpicture information is encoded as a separate subpicture data stream, which is distinct from the MPEG video presentation stream. Notably, in an MPEG formatted video presentation stream, the closed caption information is encoded as part of the MPEG video stream. Displayed subpicture information overlays the displayed video presentation and can vary in size from an icon represented by a few pixels, to full screen animation.
During playback of an MPEG formatted video presentation distributed on DVD, trick modes can include speedup or slowdown of normal playback speed to either search for a specific location on the disc or to look at details of a clip that would normally be missed at normal speed. By convention, normal playback speed can be denoted as 1×. Both audio and video trick modes are possible and both can be found on commercially available DVD players. However, conventional methods for playback of captioning information during video trick modes have proved to be problematic. In general, closed captioning information and features are deactivated during trick modes in order to overcome the many problems associated with playback. Notably, since the trick modes playback can include the removal, addition or repetition of video and/or audio frames, it can be difficult to synchronize the closed caption information with the trick mode video and/or audio segment.
Disabling captioning during trick modes is not an entirely satisfactory solution as the caption content can be of interest during such trick modes. Accordingly, it would be advantageous if a DVD player could display caption content in a manner that overcomes the limitations of the prior art and achieves a desirable and worthwhile experience during video trick modes.